【 Flutter 】Flutter を 基礎 から 学習 ( ウィジェット編 ) part119 アニメーション系ウィジェット

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(home: new MyHomePage()));
}

class MyHomePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _MyHomePageState();
  }
}

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  AnimationController? _controller;

  Animation<double>? _animation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      vsync: this,
      duration: const Duration(seconds: 3),
    );

    _animation = _controller!.drive(
      Tween(begin: 0, end: 300),
    );
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'テスト中！',
      theme: ThemeData(primarySwatch: Colors.blue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: Stack(
            children: <Widget>[
              AnimatedBuilder(
                animation: _animation!,
                builder: (context, child) {
                  return Container(
                    height: _animation!.value,
                    width: _animation!.value,
                    // 引数からFlutterLogoのインスタンス(コレ)が渡されるにでキャッシュの心配は不要です。
                    child: child,
                  );
                },
                // コレ
                child: const FlutterLogo(),
              )
            ],
          ),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            _controller!.forward();
          },
          child: Icon(Icons.add),
        ),
      ),
    );
  }
}